In numerous mechanical systems having fluid reservoirs, there has been a continuing need for economical, convenient and reliable indicating systems to indicate the fluid level in such reservoirs. For example, in automobile engines and other internal combustion engines requiring a continuous circulation of lubricating fluid such as oil, indicator systems have been necessary to measure and indicate the oil level in the engine crankcase for the usual purpose of operational maintenance. Without such an indicating system, the operator would have no convenient way of ascertaining when to add oil to keep the crank case oil level at a suitable operating level or how much oil to add.
The most common such indicating system in use today is the well-known dip stick which is employed universally by the automobile industry. Other more sophisticated remote indicating systems have been used on special purpose automobiles such as race cars and other specialty engines of high value. For example, one such indicating system is similar to the standard automobile fuel level measuring system which consists of a float assembly, an electrical position sensor to sense the position of the float, and an electrically actuated dashboard meter to indicate oil level.
In general, the dip stick, although effective, is also inconvenient because it requires locating the dip stick handle amongst the clutter of a tightly packed engine compartment, pulling the dip stick entirely out of its sleeve to wipe splashed oil off of it, finding the open end of the sleeve to reinsert the dip stick, (which usually requires holding on to the long hot and oily end of the dip stick), again pulling the dip stick out, and then trying to read the often confusing oil splotches on the dip stick with reference to the oil level indicia thereon. This procedure is dirty, cumbersome and often intimidating to many people. As a result, frequent checks of crankcase oil level often may be neglected to the detriment of engine maintenance requirements. Alternative types of systems such as the float assembly and remote indicating meter characterized above usually have been considered uneconomical for use on most automobiles, especially since road automobiles are not driven at the limits of performance and continuous monitoring of crankcase oil level therefore is not necessary.
Other fluid level indicating systems are also known in the prior art. For example, U.S. Pat. No. 1,526,376, issued Feb. 17, 1925 to Rosenmund, discloses a liquid level indicator for measuring the oil within the crankcase of an automobile engine, according to which the pulling up of a handle indicates the height or level of oil in the crank case. In the Rosenmund structure, a float valve is actuated by movement of the actuator handle to close off an orifice and thereby confine a volume of oil within a portion of a vertical tube that is connected to the crankcase. One might analogize Rosenmund as a device for mechanical "reading" of the oil level in an otherwise well known sight glass.
U.S. Pat. No. 1,830,116, issued Nov. 3, 1931 to Kruft, discloses a liquid level gauge which utilizes the differential cross-sectional areas of a pair of connected tubular elements, and the differential displacement of oil therein, to move an indicator pointer with respect to an indicia-bearing plate, to thereby indicate liquid level.
U.S. Pat. Nos. 3,981,324, issued Sept. 21, 1976 to Wearing, and 2,618,975 issued Nov. 25, 1952 to St. Chair, disclose other types of level gauges, and U.S. Pat. No. 4,141,310, issued Feb. 27, 1979 to Rich, Jr., discloses an apparatus for indicating the desired finish level of a poured (e.g. concrete) floor at a given location.
In spite of the prior efforts at developing improved fluid level indicators, there remains a need in the art, and especially in the automotive arts, for an economical, reliable, easily utilized level indicator that will permit convenient intermittent checking of a fluid level without unnecessarily exposing the user to engine dirt and without adding an additional indicator to the already cluttered dashboards of modern automobiles. An improved level indicator with these qualities would have significant impact in improving the quality of auto maintenance by making periodic crankcase oil level monitoring a far less troublesome chore than it has been heretofore.